WASHINGTON — Brett McGurk, the U.S. special envoy for the coalition to defeat ISIS, has quit in protest of President Donald Trump's decision to pull out of Syria and essentially abandon the Kurdish forces there, three U.S. officials confirmed to NBC News.

McGurk informed Secretary of State Mike Pompeo on Friday evening of his decision, according to two State Department officials. His resignation is effective Dec. 31.

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McGurk, who worked in the George W. Bush White House, was a holdover in the anti-ISIS position from the Obama administration where he was appointed to his current role in 2015. News of his resignation was reported earlier by CBS.

Trump said in a tweet Saturday night that McGurk "was supposed to leave in February, but he just resigned prior to leaving. Grandstander?"

Despite serving for the previous administration, Trump had kept him on in a job that entails coordinating the dozens of other countries that the U.S. enlisted to join in fighting ISIS in Iraq and Syria.

Fewer than two weeks ago, McGurk said at a press briefing that it would be irresponsible to leave Syria in the near future, as ISIS had not yet been defeated.

“Obviously, it would be reckless if we were just to say, well, the physical caliphate is defeated, so we can just leave now. I think anyone who’s looked at a conflict like this would agree with that.”

“We have won against ISIS,” Trump said in a video recorded on the White House lawn. “We’ve beaten them, and we’ve beaten them badly and we’ve taken back the land, and now it’s time for our troops to come back home.”

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Trump’s decision left McGurk flat-footed, unable to explain to U.S. allies who have been fighting ISIS with the United States why they were neither consulted nor informed in advance. Nor have senior Trump administration officials been able to tell allies and Kurdish forces whether U.S. air strikes will continue in Syria to support the mission against ISIS.

Nick Rasmussen, former director of the National Counterterrorism Center, said it was understandable that McGurk would feel he had no choice but to leave.

“It would be quite difficult for him to carry on further conversations with any of our partners around the world,” said Rasmussen, an NBC News and MSNBC contributor. “What would he say to them right now other then ‘I’m sorry’ or 'I wish it weren’t this way?’”

He said Trump’s move on Syria makes it impossible for those in envoy roles like McGurk’s to make or seek commitments from foreign allies, because it’s impossible to know whether U.S. commitments will be kept.

When reached for comment about Brett McGurk’s resignation, a senior administration official wouldn’t speak on the record. Instead, the official with the National Security Council disparaged McGurk, saying he should have been fired long ago. The official noted with derision that McGurk worked for the Obama administration but said nothing about McGurk’s years of service during the Bush presidency. The official did not say why McGurk should have been fired or why he wasn’t terminated earlier.